The present invention relates to improvements in a signal transmission system.
The latest automatic control is being developed in its course of enabling the complicated high degree control with the electronic computer and digital integrated circuitry. With signals from conventional signal transmitters received by signal receivers operatively coupled to electronic computers and digital integrated circuitries, there have been encountered difficult problems in potential differences, noise, grounded points etc. and various counter-measures thereto have been already proposed. For example, a relay device has been used to connect the signal transmitter to the signal receiver to maintain the transmitter electrically insulated from the receiver. The use of the relay has been attended with the mechanical operation resulting in a delay of the transmission time, a decrease in useful life of mechanically operating components, the chattering of contacts etc. In order to avoid these objections, the signal transmitter might be connected in electrically insulating relationship to the signal receiver through the utilization of the optical coupling. In the latter event the use of a light emitting diode as a current-to-light transducer has led to the necessity of connecting a filter to the signal transmitter to prevent malfunction due to noise superposed on a signal from the transmitter resulting in an expensive construction. Also with an incandescent lamp used in place of the light emitting diode, the lamp has been required to be often replaced by a new lamp because it is short in useful life although the filter is omitted. Further the maintenance has consumed much labor.